1. Field of the Invention
The present invention relates to an image processing apparatus, and an apparatus capable of transmitting an image signal.
2. Related Background Art
In place of the conventional optical camera utilizing silver halide emulsion, there has been developed an electronic still camera in which an object image is converted into electric signals by an image pickup device and is recorded on a magnetic recording medium. There has also been developed an electronic still camera having a function of image reproduction. In such a conventional electronic still camera, the image signal is read from the image pickup device in synchronization with the rotation of a magnetic disk constituting the recording medium. The color difference signal is converted into a line-sequential signal, and the brightness signal and the line-sequential color difference signal are respectively frequency modulated, then frequency multiplexed and recorded on the magnetic disk.
In the reproducing circuit, the output of a magnetic head is separated by filters into a brightness component and a line-sequential color difference component, which are respectively frequency demodulated to obtain the brightness signal and the line-sequential color difference signals. The line-sequential color difference signals are converted into line-simultaneous signals by a line-simultaneous circuit consisting of a line sense circuit, a line delay circuit and switches. The obtained brightness and line-simultaneous color difference signals are converted by an NTSC encoder into an NTSC image signal which is supplied to an NTSC image monitor, whereby a reproduced image can be obtained.
Also, in case of transmitting the image, recorded on the magnetic disk to another location, the transmitting apparatus stores said image in a frame memory after separating it into color component signals of R, G and B, then reading said signals in a predetermined order and sends said signals to a telephone line after conversion into an analog signal by a D/A converter.
The conventional structure consumes much electric power because of the use of a 1H (one horizontal synchronization period) delay line in the line simultaneous circuit and for the skew compensation in the field reproduction. While the reproduced image is displayed on the monitor, the magnetic disk has to be constantly rotated, thus requiring additional power consumption. Consequently, there is required a battery of a considerably large capacity, in comparison with w that in a camera with recording function only.
Also in case of transmitting the taken image, for example, through a telephone line, there is also required a transmitting apparatus for reproducing and transmitting the image recorded on a magnetic disk, but such transmitting apparatus, if constructed as a separate unit, is wasteful because it contains many components and circuits which are common with those in the electronic still camera.
Although the foregoing explanation is limited to a conventional electronic camera utilizing magnetic disks, such drawbacks are encountered also in other various image processing apparatus, such as a facsimile apparatus with a monitor unit, or a television telephone.
In the electronic still camera handling still images or in the movie camera handling moving image, the image signal is often obtained in some places in the form of primary or complimentary colors, and in other places in the form of a brightness signal and color difference signals. The actual signal processing is often conducted by common hardware, such as image memories or digital signal processors (DSP). For storing the image signal in the image memory, an A/D converter is required for converting the analog signal into a digital signal. For this purpose, there is already known a circuit structure utilizing two A/D converters for the brightness signal and the color difference signals, in which the image signal of primary (or complementary) colors is converted into brightness signal and color difference signals, which are then converted into digital signals by said A/D converters. Also, there is known a circuit structure utilizing an A/D converter capable of high-speed digitization of a serial image signal of primary (or complementary) colors, wherein the digitized signal is converted into the brightness signal and color difference signals in or after the image memory
In either conventional structure, for effecting the A/D conversion in order to process the image signal of primary or complimentary colors and the image signal composed of brightness signal and color difference signals by means of a common digital processing circuit, there is required a conversion circuit for signal conversion into either signal form, and/or a high-speed A/D converter capable of digitizing at least the brightness signal, or preferably the serial signal of primary colors (for example RGB dot-sequential signal).
Such a high-speed A/D converter has drawbacks of a large circuit structure and high power consumption, and, when used in combination with an A/D converter of a relatively low speed, it is extremely difficult to match the characteristics (reference voltage, non-linearity etc.) of these A/D converters.
Besides, the conventional circuit structure is inevitably complex because exclusive circuits are required for the signal compression at recording and for the signal expansion at reproduction.